Abstract: The meteorological elements under special terrain were simulated by the mecoscale numerical model, and the fine diffusion characteristics for an atmospheric environment risk event were simulated by the CALPUFF model. The results show that surface wind direction is parallel to the valley direction. The west-north and east-south wind and north wind prevail in Huangshui river valley and in Beichuan river valley, respectively. Strongly hillside daytime radiative heating and night cooling effect in Qinghai-Tibet plateau lead to inversion layer frequently with high intensity, and the frequency of inversion temperature reaches 36%, while the maximum intensity increases 2.0 ℃ every the 100 m height, which is not favorable to diffuse pollutants in vertical direction. By simulation, temperature in same height hillside is about 1.5 ℃ higher than in the center of valley. CALPUFF plume trajectory model can be applied to the simulation of atmospheric environmental risk events, and the simulation results clearly depict the initial condition and detailed distribution about pollutant transport and diffusion along the valley. Under the complex terrain and weather conditions, some diffusion phenomena will appear such as puff is hindered by the mountain, puff diffusion locus accords to the characteristic and regulation from stream affection and puff diffusion is influenced by circulation of valley wind, which have important significance to estimate the diffusion, influencing range and extent for atmospheric environmental risks in the city.

Key words: font-family: "Times New Roman", mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, Valley')">mso-fareast-font-family: 宋体">Valley, Complex terrain, Inversion temperature, Environmental risk